African-American citizens are being failed by the US criminal justice system because of ingrained racial bias in the way suspects are treated, according to the head of the United States’s largest legal professional body.

Paulette Brown, who became the first black female president of the American Bar Association (ABA) in August, is determined to transform the negative image that many people hold of lawyers.

Speaking to the Guardian during a visit to London for the formal opening ceremonies of the legal term at Westminster Abbey and in parliament, Brown said one of the priorities of her year in office would be to lead the drive to encourage the ABA’s 400,000 members to carry out more voluntary, pro-bono work.

But after going to Ferguson, Missouri , and other places where there have been protests over the treatment of black suspects, she has also become more concerned about the way defendants are processed through US courts.

“One in 16 African Americans are subjected to the criminal justice system,” Brown explained, “compared to one in 106 of white people. A lot of that is drugs. The evidence, however, shows that black people don’t use drugs any more [than white people].

“But they are being arrested for it and charged with it [more frequently] and some of that is implicit bias – particularly on the part of prosecutors. Prosecutors are overcharging.” She added: “Ninety-five percent of all prosecutors are white; 88% of all lawyers in US are white.”

Brown, who was brought up in Baltimore, moved to New Jersey where she specialised in commercial litigation and employment defence. She has also served as a municipal court judge for three years.

“In our system, prosecutors have so much control – sometimes more than the judges,” she added. “They decide whether someone is to be charged with a crime and what crime that will be. The judge doesn’t have discretion. The prosecution has so much power so they have a bad reputation in the community.

“Public defenders think they are really the do-gooders, but are they encouraging a group of people to plead to higher offences than others? For example, there’s no evidence that black people use drugs more than whites, but they are arrested at a rate more than six times than that of their white counterparts for drug use.”

Public defenders, she added, do not have the same resources as prosecutors – nor are they paid as much, “so you are sending a message saying that public defenders are not as important”.

Brown said the ABA is supporting efforts to redress the “implicit bias in the justice system”. Sometimes public defenders, she said, might be representing two people – one white, one African American – and they may enter a “less favourable plea deal for the brown character. There are so many subconscious messages that are given to us that say white is good and black bad.

“During Hurricane Katrina, for example, when you saw an image of black people with food, they were [said to be] looting. When you saw an image of white people with food, they had found it for their family. Sometimes it’s subliminal.”

If any good had come out of the confrontations in Ferguson and elsewhere, she said, “it was that people from all sorts of backgrounds got riled up about it: lawyers, prosecutors and police are willing to [accept] they may have bias”.

Brown also pointed out that 53% of African-American youths who are arrested under the age of 18 are charged as adults. “Sometimes,” she said, “they [charge people as young] as 13 or 14 year olds and treat them as adults.

“[That means] they go to a completely different court and have trials by jury as opposed to being in a juvenile court. The prosecution have the discretion to charge them as adults; in some states there’s legislation pending saying there should be a minimum age threshold.”

Brown said she would like to talk to Barack Obama about the US’s prison population, which is the largest in the world. “We are beginning to recognise there’s a problem of over-incarceration.”

If she hasn’t spoken to Obama, Brown has, at least, met the Queen . Both were at Runnymede in June for the 800th anniversary of the signing of Magna Carta. “I shook hands with the Queen,” she recalled. “We chatted for about 30 seconds. She knew who I was. It was fantastic. She was very happy I was there.”

The mediaeval charter remains a more potent cultural icon for Americans than for Britons. “We were taught about Magna Carta at my elementary school,” Brown said with pride.

The role of pro-bono work is becoming more important on both sides of the Atlantic. In the UK, the new justice secretary, Michael Gove , has called on British lawyers to do more voluntary work to ensure justice is available for all.

In the US, mandatory pro-bono work is becoming more common. “There’s now mandatory pro-bono work of 50 hours a year for new lawyers in the year they qualify in New York before they get their full licence,” she explained.

“Many states have mandatory pro-bono work. They assign a case for you every year which has to be done on a pro-bono basis; usually one day’s court work. They give you written instructions, but the instructions are often pretty basic. If you don’t do it, you get done for contempt.

“[But] lawyers still have to be able to earn a living. While it’s wonderful that lawyers do pro-bono work, it’s not a substitute [for all funded legal representation] and they can’t fill that gap completely.”